Typically, automotive vehicles are provided with an engine cooling system including a heat exchanger, such as a radiator. When the engine is running, heat is transferred from the engine to a coolant that flows through the engine. The coolant then flows from the engine to the heat exchanger through a series of conduits. At the heat exchanger, heat is transferred from the coolant to cooler air that flows over the outside of the heat exchanger. This process repeats itself in a continuous cycle, thereby cooling the engine.
A typical heat exchanger includes a series of tubes supported by two chambers or headers positioned at either end of the heat exchanger. The headers are usually joined to the tubes by means of brazing. During operation of the engine and cooling system, the tubes are subject to thermal cycling (rise and fall of the temperature of the heat exchanger components) which leads to stresses as neighboring tubes may expand to different degrees such that axial loads are imposed on tubes by their neighbors.
In many systems, the tubes comprise a single enclosed channel. The tubes have a generally elongate, substantially rectangular cross-sectional shape, and comprise two opposing longer sides, or faces, and two opposing curved shorter sides, or noses. Within the heat exchanger, the tubes are arranged side by side with the faces of neighboring tubes opposing each other and defining a space or passage between the tubes through which air can flow. This geometry of the tubes is, therefore, favorable as it creates a relatively large surface area over which the cooler air can pass whilst minimizing the disruption to the air flow through the heat exchanger. However, these types of header/tube combinations are prone to failure because of the stress concentrations that occur along the header/tube joint, in particular around the noses of the tubes.
To overcome some of the disadvantages of single channel tubes, a number of tube designs have been developed in which the tubes are formed from a folded sheet of metal. These folded tubes, or ‘B-tubes’, have a longitudinal seam separating two channels. The overall cross-sectional shape of these tubes is, however, substantially the same as that of the single channel tubes to benefit from the large surface area and minimal disruption to air flow.
These folded tubes, however, still possess a number of disadvantages. Firstly, the cross-sectional area of the tube dictates the required dimensions of the headers. In particular, the longer cross-sectional dimension of the tubes dictates the minimum width of the headers, and thereby the minimum width of the heat exchanger. Secondly, the elongate cross-sectional shape of the tubes creates a narrow opening at the end of the tube that generates undesirable entry and exit pressure losses. Thirdly, although the design of the folded tubes is known to reduce the likelihood of failure of the header/tube joint around the nose of the tubes, the small radius of the nose of each the tubes still leads to stress concentrations in these regions.
It is, therefore, an object of the present invention to provide an improved tube for a heat exchanger that overcomes these problems.